1. Field of the Invention
The present invention relates to low k dielectrics, and more particularly, to a carbon doped oxide having a carbon doping concentration that is graded.
2. Background Information
As integrated circuit technology advances, integrated circuit devices become smaller and smaller. This allows for greater speed and increased device packing densities. Sizes of individual features, for example the transistor gate length, on modern integrated circuits is shrinking to less than 50 nanometers. The resultant increase in packing densities has greatly increased the number and density of metal interconnects on each chip.
The metal interconnects (which consist of conducting lines and vias) have become smaller, more complex, and more closely spaced. The smaller sizes of the interconnect pitch leads to RC (resistance-capacitance) coupling problems which include propagation delays and cross talk noise between interlevel and intralevel conductors. RC delays thus limit improvement in device performance. Additionally, fringing electrical field effects near the metal lines may adversely affect performance of the interconnects.
Capacitance can be reduced by employing low dielectric constant (low k) dielectric materials to insulate the metal interconnect lines. Since capacitance is directly proportional to the dielectric constant of the insulating material, the RC delay can be reduced when a low k material is used. Various semiconductor equipment manufacturers have developed low k dielectrics. One of the most promising low k dielectrics is the carbon-doped oxide (SiOxCyHz).
While carbon doped oxide (CDO) film has been found useful to reduce capacitance by lowering film density and polarizability of bonds, CDO film has poor thermal and mechanical properties. For example, CDO exhibits poor hardness, is susceptible to cracking, and has low thermal conductivity.